Ferrite (Fe3O4) nanoparticles coated with biocompatible chitosan were synthesized for use as an MRI (magnetic resonance imaging) contrast agent. The coating was performed simultaneously with the synthesis of the ferrite nanoparticles. A dynamic light-scattering spectrometer (DLS) and a transmission electron microscope (TEM) were used to measure the average diameter of the coated nanoparticles, which was 67.0 nm. Fourier transform infrared (FT-IR) measurements showed strong bonding of the chitosan molecules to the surface of the ferrite nanoparticles. The spin-lattice (T1) and spin-spin (T2) relaxation times of nuclear spins (hydrogen protons) in the aqueous solution of various concentrations of coated ferrite nanoparticles were determined using a nuclear magnetic resonance (NMR) spectrometer. Using these data, we found that the T1 and T2 relaxivities of nuclear spins in the aqueous solution of ferrite nanoparticles were 0.00291 and 0.0691 ppm-1sec-1, respectively. In particular, the value of the T2 relaxivity was much larger than that of the commercial contrast agent of GD-DTPA (Gadolinium diethylenetriamine penta-acetic acid). A 31.7% intensity loss in the T2 image of rabbit liver was observed after injecting the aqueous solution of coated nanoparticles into the rabbit, which shows that our coated ferrite nanoparticles can be used as a T2 MRI contrast agent.